Optical apparatus for dual-beam laser texturing

ABSTRACT

A disk texturing tool is used, for example, to provide textured spots in an annular portion of both sides of a hardfile disk. Disks are moved into and out of the texturing process in cassettes, through two disk-handling stations. An optical system includes a laser directed at a beamsplitter to split the laser beam into two beams having approximately equal power, which are directed along parallel paths through a power control optics block to expose simultaneously opposite sides of a disk to be textured. The power control optics block includes means for attenuating and measuring each of the two beams. A shuttling mirror directs these two beams alternately at a disk within each of the two disk handling stations.

CROSS-REFERENCE TO A RELATED APPLICATION

A co-pending U.S. application, Ser. No. 08/150,525, filed Nov. 10, 1993,entitled "Procedure Employing a Diode-Pumped Laser for ControllablyTexturing a Disk Surface," by Peter M. Baumgart, et al., having a commonassignee with the present invention, the disclosure of which is herebyincorporated by reference, describes a process for creating a "distantbump array" surface texture in a magnetic recording disk for reducingstiction, together with the disk so textured. The texturing process usesa tightly focused diode-pumped Nd:YLF or Nd:YVO₄ or other solid-statelaser that is pulsed with a 0.3-90 nanosecond pulse train to produce aplurality of distantly-spaced bumps in the disk surface. The bumpcreation process is highly controllable, permitting repeated creation ofa preselected bump profile, such as a smooth dimple or one with acentral protrusion useful for low stiction without close spacing orelevated "roughness." Some bump profiles permit texturing of thedata-storage region of the disk surface for low stiction withoutmaterially affecting magnetic data storage density. The application,Ser. No. 08/150,525 has been abandoned and continued as Ser. No. 601,887on Feb. 15, 1996, with a divisional application, Ser. No. 457,559 beingfiled from the original application on Jun. 1, 1995, and with acontinuation, Ser. No. 889,348, of the divisional application beingfiled on Jul. 8, 1997.

Another co-pending U.S. application, Ser. No. 08/613,564, filed Mar. 11,1996, which as subsequently issued as U.S. Pat. No. 5,658,475, entitled"Apparatus for Laser Texturing Disks," by Michael Barenboim, et al,having a common assignee with the present invention, further describes alaser texturing station in which the optical apparatus of the presentinvention may be used.

Another co-pending U.S. application, filed on an even day herewith,Docket Ser. No. 08/707,384 entitled "Apparatus and Method forControlling a Laser Texturing Tool," and having a common assignee withthe present invention, describes both electronic hardware and softwareused to control a laser texturing station in which the optical apparatusof the present invention may be used.

Another co-pending U.S. application, filed on an even day herewith, Ser.No. 08/707,385, entitled "Controlling Pulses in a Laser Texturing Tool,"and having a common assignee with the present invention, describes amethod for controlling the laser used with the optical apparatus of thepresent invention.

Another co-pending U.S. application, filed on an even day herewith,Docket Number BC9-96-046, which has been abandoned, entitled "Method forControlling Laser Power in a Texturing Process," and having a commonassignee with the present invention, describes a program for setting andmaintaining the laser power levels in the optical apparatus of thepresent invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to apparatus for fabricating a disk, such as amagnetic recording disk used in a computer hard disk drive, havingsurfaces textured by exposure to a pulsed laser, and, more particularly,to optical apparatus for splitting the output beam from such a laserinto a pair of sub-beams of equal, controlled intensity, which areindividually directed along equal-length paths to opposite sides of thedisk being textured.

2. Background Information

Current hard disk drives use a Contact Start-Stop (CSS) system allowinga magnetic head, used to read and write data, to contact the surface ofa magnetic disk in a specific CSS region when the disk is stationary.Thus, before the rotation of a spinning disk has stopped, the magnetichead is moved to the CSS region, where the magnetic head settles on thesurface of the disk. When the disk again starts to rotate, the magnetichead slides along the disk surface in this region, until the laminar airflow at the disk surface, due to its rotation, fully lifts the magnetichead from the disk surface.

After the magnetic head is lifted in this way, it is moved from the CSSregion to another region of the disk to read and write data. The CSSregion is preferably textured to minimize physical contact between themagnetic head and the disk surface. In this way, the contact stick-slipphenomenon often called "stiction" and other frictional effects areminimized, along with the resulting wear of the magnetic head surface.Outside the CSS region the remainder of the disk surface preferablyretains a specular smoothness to permit high-density magnetic datarecording.

3. Description of the Prior Art

U.S. Pat. No. 5,062,021, to Ranjan et al., describes a process in whichmagnetic recording media are controllably textured, particularly overareas designated for contact with data transducing heads. In conjunctionwith rigid disk media, the process includes polishing an aluminumnickel-phosphorous substrate to a specular finish, then rotating thedisk while directing pulsed laser energy over a limited portion of theradius, thus forming an annular head contact band while leaving theremainder of the surface specular. The band is formed of multipleindividual laser spots, each with a center depression surrounded by asubstantially circular raised rim. The depth of the depressions and theheight of the rims are controlled primarily by laser power and firingpulse duration. The shape of individual laser spots can be altered byvarying the laser beam inclination relative to the disk surface. On alarger scale, the frequency of firing the laser, in combination withdisk rotational speed controls the pattern or arrangement of laserspots. The smooth, rounded contours of the depressions and surroundingrims, as compared to the acicular character of mechanical texturedsurfaces, is a primary factor contributing to substantially increaseddurability of laser textured media.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided apower control optics block for balancing the power in a pair of parallelpolarized laser beams. The optics block includes an optical path throughwhich each of the laser beams is directed, an attenuation mechanismdisposed along each of the two optical paths, and a power detectionmechanism disposed along each of the two optical paths. The two opticalpaths extend in a parallel, spaced-apart relationship. The attenuationmechanism controls the output power in the optical path extending withinit. The power detection mechanism measures an output power level in theoptical path extending through it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an internal portion of a prior-art disk driveunit, including a rotatable magnetic disk having a textured annularregion for CSS operation, and a magnetic head;

FIGS. 2 and 3 are transverse cross-sectional views of individualtextured spots, which form examples of spots which may be made using theapparatus of the present invention, with the spot of FIG. 2, beingformed particularly according to the method of U.S. Pat. No. 5,108,781,and with the spot of FIG. 3 being formed particularly according to themethod of co-pending U.S. Application, Ser. No. 08/150,525.

FIG. 4 is an isometric view of a laser disk texturing tool built inaccordance with the present invention;

FIG. 5 is a cross-sectional plan view of the tool of FIG. 4, taken asindicated by section lines V--V in FIG. 4 to show disk-handling andlaser-texturing stations thereof;

FIG. 5A is a longitudinal cross-sectional view of a beam expander in thetool of FIG. 4;

FIG. 5B is a partially sectional plan view of a beam splitter and powercontrol optics block in the tool of FIG. 4;

FIG. 5C is a plan view of beam directing apparatus adjacent a disk beingtextured within the tool of FIG. 4;

FIG. 6 is a cross-sectional side elevational view of the tool of FIG. 4,taken as indicated by section lines VI--VI in FIG. 5 to show mechanismsused to handle cassettes holding disks for texturing;

FIG. 7 is a cross-sectional rear elevational view of the tool of FIG. 4,taken as indicated by section lines VII--VII in FIG. 5 to show themechanism used to transfer disks from cassettes within the disk-handlingstations to the laser-texturing station and to return the disks to thecassettes; and

FIG. 8 is a longitudinal cross-sectional view of an end portion of aspindle, used to move disks through the texturing process in the tool ofFIG. 4.

FIG. 9 is a cross-sectional plan view of a slider used to move cassettesfilled with textured disks from one conveyer to another in the tool ofFIG. 4;

FIG. 10 is a block diagram of electronic apparatus for controlling thepower level within laser beams within the tool of FIG. 4; and

FIG. 11 is a flow chart of a program executed in the microcontroller ofFIG. 10.

DETAILED DESCRIPTION

FIG. 1 is a plan view of a portion of a disk drive unit from the priorart for a computing system, including a rotatable magnetic storage disk10, together with a magnetic head 12, which is driven in a generallyradial direction relative to the disk 10 by means of a drive arm 13.This disk 10 is an example of the type of product which can be madeusing the apparatus of the present invention. When the disk drive unitis in operation, disk 10 is rotated about its central hole 14, forming alaminar flow of air holding magnetic head 12 slightly away from theadjacent disk surface 16. Before this rotation is stopped, magnetic head12 is driven to be adjacent to a textured annular region 18 of thesurface of disk 10. As this disk rotation slows and stops, thefrictional and stiction effects occurring between the surface of annularregion 18 and the adjacent contacting surface of magnetic head 12 areminimized by the textured nature of the surface of this region 18.Subsequently, when the rotation of disk 10 is restarted, these effectsare again minimized, as the rate of rotation of disk 10 increases untilthe laminar flow of air near its surface lifts the adjacent surface ofmagnetic head 12 completely away from the disk surface. Thus, as therotation of disk 10 is stopped and subsequently restarted, the wear ofthe surface of magnetic head 12 is minimized. Disk 10 is preferably adouble-sided magnetic storage disk, with a second side, opposite theside shown in FIG. 1, having similar features.

FIGS. 2 and 3 are transverse cross-sectional views of individualtextured spots, which form examples of spots which may be made using theapparatus and method of the present invention.

FIG. 2 shows a portion of a disk surface roughened by the prior-artmethod taught by Ranjan, et al., in U.S. Pat. No. 5,062,021. With thismethod, a portion of the disk surface to be roughened is exposed to apulse of laser light. The surface is heated rapidly, so that a part ofthe surface material is melted and then rapidly cooled, changing thesurface topography to include a generally round central depression 24below the nominal surface plane 26 and a generally round peripheralridge 28 above this plane 26. The process described by Ranjan, et al.produces a ring of textured spots of this kind by repeatedly firing alaser as the disk being textured is rotated. The laser is then displacedradially through a pitch distance, and a second ring of textured spots,concentric with the first ring thereof, is produced. This process isrepeated until texturing fills the annular region to be textured. Thenature of each individual textured spot is determined primarily by thepeak energy at which the laser is fired together with the pulse width.The distance between textured spots on the ring is determined by therelationship between the rate at which the laser is fired and therotational speed at which the disk is turned.

FIG. 3 is a transverse cross-sectional profile of a laser textured spotproduced using the method of the previously-described co-pending U.S.patent application, Ser. No. 08/150,525. The heights of surfacefeatures, compared to their widths, are exaggerated. A centralprotrusion 30 rises above the depth of the ring depression 32,preferably to a height somewhat greater than the height of thesurrounding peripheral ring 34. The heights of the protrusion 30 andring 34 above the nominally level surface 35 before texturing aredetermined by various laser and disk-material parameters, such as laserfluence, pulse width, spot size, and disk surface composition.

FIG. 4 is an isometric view of a laser-texturing tool 37, built inaccordance with the present invention, which is used to applylaser-texturing to disks in a non-stop production mode as long ascassettes filled with disks are loaded and unloaded at a sufficientrate. These cassettes move through a right disk-handling station 38 anda left disk-handling station 39, with individual disks from thesestations 38 and 39 being alternately textured by a single laser assemblyin a laser-texturing station 40. A modular configuration allows the tool37 to continue running, at a reduced rate of production, even if one ofthe disk-handling stations 38, 39 cannot be used.

The laser-texturing tool 37 is a self-contained system, with necessaryelectrical, electronic, and pneumatic components located in a basesection 41 and in a pair of instrumentation cabinets 42. Variouscontrols and output devices are placed on a slanted control panel 43.Since the infrared laser used in the texturing process producesinvisible, potentially-harmful rays, a laser-texturing station 40 ishoused in a light-tight cabinet within the tool 37, with a safety switchoperated by the opening of each access door 44 turning off the laser.Furthermore, these doors 44 can be opened only when the tool is in amaintenance mode. The tool 37 is switched between automatic andmaintenance modes by turning a mode switch (not shown) on control panel43. Two television cameras (not shown), mounted within thelaser-texturing station, allow the process to be viewed on a pair ofmonitors 45.

The upward-opening doors 46 of disk-handling stations 38 and 39,providing access for loading and unloading cassettes holding disks, arenot interlocked, and may be opened or closed at any time, even duringthe operation of the texturing process. Within the tool 37, rays fromthe laser are blocked from the areas in which these cassettes are loadedand unloaded.

FIG. 5 is a horizontal cross-sectional view of laser-texturing tool 37,taken as indicated by section lines V--V in FIG. 4, to revealparticularly disk-handling stations 38, 39 and the laser-texturingstation 40. Left disk-handling station 39 is a mirror image of rightdisk-handling station 38. Each disk-handling station 38, 39 has an inputconveyor 47 carrying cassettes 48 loaded with disks 49 to be textured,rearward, in the direction of arrow 50. Each cassette 48 has a number ofpockets 51 in which disks 49 are loaded in a vertical orientation, and alower opening 52 allowing the removal of individual disks by liftingfrom below. While FIG. 5 shows cassettes having only five disks, forclarity, in reality a cassette for this system typically holds 25 disks.

FIG. 6 is a cross-sectional side elevational view of the tool of FIG. 4,taken as indicated by cross-section lines VI--VI in FIG. 5, to show theconveyor systems moving cassettes filled with disks into and through theprocess. The tool operator loads a cassette 48 filled with disks 49 tobe textured by opening the access door 46, which pivots upward along itsrear hinge 53. The cassette 48 is normally loaded onto a raised platform54, which, in this position holds the cassette 48 upward, in thedirection of arrow 55, away from input conveyor 47, allowing thisconveyor 47 to move another cassette 56 stored in a queue on theconveyor 47 without simultaneously moving the most-recently loadedcassette 48. FIG. 6 also shows a cassette indexing conveyor 57, whichmoves a cassette 58 in incremental motions above a disk lifter 59, sothat the disk lifter 59 can remove individual disks 49 from the cassette58 for placement into the laser-texturing process, and so that the disklifter 59 can subsequently return textured disks to the cassette 58.FIG. 6 also shows a transfer table conveyor 60, which is used in themovement of cassettes filled with textured disks from indexing conveyor57 to an output conveyor 61 (shown in FIG. 5).

FIG. 7 is a cross-sectional rear elevational view of the tool of FIG. 4,taken as indicated by section lines VII--VII in FIG. 5 to show themechanism used to transfer disks from a cassette 58 within thedisk-handling station 38 into the laser texturing process and to returntextured disks to the cassettes. FIG. 7 also provides a transversecross-sectional views of cassette indexing conveyor 57 and of outputconveyor 61.

The movement of a cassette to the point at which individual disks areremoved from the cassette to be carried into the texturing process willnow be discussed, with particular reference being made to FIGS. 6 and 7.

Thus, referring to FIGS. 5, 6, and 7, each conveyor 47, 57, 60, 61includes a belt 61a extending under each side of a cassette 48, 56, 58loaded thereon. Each belt 61a a extends between a pair of end rollers 62and above a number of idler rollers 63. At one end of each conveyor 47,57, 60, 61 the end rollers 62 are driven in either direction by a motor64. This system for cassette transport also includes a pair of lateralguides 65, ensuring that each cassette stays in place atop theconveyors, and cassette detectors 66, 66a, 67, 68, 69, which determinewhen a cassette reaches an adjacent point along a conveyor system. Eachcassette detector 66, 66a,67, 68, 69 includes a light source 69a whichis reflected off an adjacent surface of a cassette when such a surfaceis present, to be detected by a receiver 69b, which in turn provides aninput to a computing system 70 controlling the operation of the motors64 and other motors, solenoids, and valves within the laser-texturingtool 37 to effect operation as described herein.

When cassette 48 is placed on top of raised platform 54, its presence isdetected by first input cassette detector 66. Since the input conveyor47 and the system logic controlling its movement are configured to allowthe queuing of cassettes, the subsequent movement of the cassette 48 isdetermined by whether other cassettes are already present on inputconveyor 47 and indexing conveyor 57. If no cassette is already presenton these conveyors 47, 57 (i.e., if cassettes 56, 58, and 69c are notpresent), platform 54 is lowered, so that the cassette 48 rests on topof input conveyor 47, and the conveyors 47, 57 are turned on to movecassette 48 rearward, in the direction of arrow 50. When indexingcassette detector 68 detects the presence of a cassette being moved inthis way, input conveyor 47 and indexing conveyor 57 are stopped,leaving the cassette positioned so that the first of its pockets 51 inwhich diskettes 49 may be placed (i.e. the end pocket farthest in thedirection indicated by arrow 50) is directly over disk lifter 59.

On the other hand, if a cassette 58 is present on indexing conveyor 57,and if no other cassette 56, 69c is present on input conveyor 47, whencassette 48 is placed on raised platform 54, this platform 54 islowered, and conveyor 47 is turned on to move cassette 48 in thedirection of arrow 50. This movement is stopped when the presence of thecassette 48 is detected by second input cassette detector 66a, leavingthe cassette queued on the input conveyor 47, in the position in whichcassette 69c is shown.

If a cassette 58 is present on indexing conveyor 57, and if a singlecassette 69c is present on input conveyor 47, when cassette 48 is placedon raised platform 54, this platform 54 remains raised while inputconveyor 47 is turned on to move cassette 69c opposite the direction ofarrow 50 until this cassette 69c is sensed by third cassette sensor 67.Then, platform 54 is lowered, and input conveyor 47 is turned on to moveboth cassettes 48, 69c in the direction of arrow 50. This movement isstopped when cassette 69c is detected by second cassette sensor 66a,leaving both cassettes 48, 69c queued on input conveyor 47.

Finally, if all three cassettes 56, 69c, and 58 are present on conveyors47, 57 when cassette 48 is placed on raised platform 54, the movement ofcassettes does not directly ensue, leaving cassettes 56, 69c queued oninput conveyor 47 and cassette 48 queued on raised platform 54.

When the texturing process has been completed on all of the disks 49 tobe textured within the cassette 58 on indexing conveyor 57, thisconveyor 57 and transfer table conveyor 60 are turned on to move thecassette 58 rearward, in the direction of arrow 50, completely onto thetransfer table conveyor 60. This motion is stopped when the presence ofcassette 58 is detected by transfer table cassette detector 69. Ifcassette 56 is present on input conveyor 47, as determined by secondinput cassette detector 67, when cassette 58 is transferred fromindexing conveyor 57 in this way, this queued cassette 56 is moved byconveyors 47, 57 to the point at which its presence is detected byindexing cassette detector 68. If a second queued cassette 48 is presenton raised platform 54 when a first queued cassette 56 is moved frominput conveyor 47 to indexing conveyor 57, platform 54 is lowered, andthe first queued cassette 48 is driven by input conveyor 47 until thepresence of the cassette 48 is detected by second input cassettedetector 67.

The movement of an individual disk from a cassette into the texturingprocess will now be discussed, with particular reference being made toFIGS. 5 and 7.

Thus, referring to FIGS. 5 and 7, to allow the movement of individualdisks 49 through the laser-texturing process, indexing conveyor 57 movescassette 58 in a number of rearward and forward motions, in and oppositethe direction of arrow 50, sequentially aligning the individual diskpockets 51 of the cassette 58 with a disk lifter 59. Disk lifter 59includes a proximity sensing mechanism 70a, for determining whether adisk 49 is present in each pocket 51. This sensing mechanism 70aconsists of an internal light source aimed at an adjacent edge 70b of adisk present in a pocket 51 and an internal sensor detecting lightreflected from such an edge 70b. The output of sensing mechanism 70aprovides an additional input to computing system 70. Thus, cassette 58is moved to the rear, in the direction of arrow 50, by indexing conveyor57, until proximity sensing mechanism 70a indicates the presence of adisk 49 in a particular pocket 51, passing any empty pockets 51 withinthe cassette 58. When a disk is detected by proximity sensing mechanism70a, the rearward movement of cassette 58 is stopped, and the disklifter 59 moves upward, in the direction of arrow 55, carrying the disk49 which is aligned the lifter 59 upward for transfer to apick-and-place mechanism 71.

Pick-and-place mechanism 71 has an arm 72 rotatable about the axis of adrive shaft 73, in and opposite the direction of arrow 74, in 180-degreeincrements. This rotation is effected by the incremental operation ofarm drive motor 75. At each end of arm 72, a pair of grippers 77, 78 ismovable between an open position, in which grippers 77 are shown, and aclosed position, in which grippers 78 are shown, by means of a pneumaticactuator 79. When a pair of grippers 77, 78 is in the closed position, adisk placed between the grippers is held by four points around itsperiphery. When the pair of grippers is opened, a disk held in this wayis released. The pick and place mechanism 71 is also moved rearward, inthe direction of arrow 50, into a position in which disks are picked upand released, and forward, in the direction opposite arrow 50, into aposition in which arm 72 is rotated.

The upward movement of disk lifter 59 carries a disk 49, which is to betextured next, upward into the location indicated by phantom line 82.This motion, which brings the disk 49 into vertical alignment with theopen grippers 77 of arm 72, occurs with pick and place mechanism 71 inits forward position (i.e., moved opposite the direction of arrow 50),allowing the upward passage of disk 49 past grippers 77. At this point,the disk rests within a groove 84 of the lifter 59. Next, pick and placemechanism 71 moves in the direction of arrow 50 to its rearwardposition, aligning the open grippers 77 with the edge of disk 49. Then,grippers 77 are closed, grasping the disk 49. Disk lifter 59 nextdescends to disengage from the periphery of disk 49. Next, pick andplace mechanism 71 moves opposite the direction of arrow 50 to itsforward position, and the arm 72 rotates 180 degrees in the direction ofarrow 74, placing disk 49 in the position indicated by phantom line 83,in axial alignment with a spindle 86 of a spindle assembly 88. Then,pick-and-place mechanism 71 returns in the direction of arrow 50 to itsrearward position, placing the disk 49 on the end of spindle 86.

FIG. 8 is a longitudinal cross-sectional view of the end of spindle 86,which includes a rotationally-driven outer cylinder 89, in which aninternal shaft 90 slides axially, in and opposite the direction ofrearward-pointing arrow 50. A sliding bushing 91 and a piston 92, and afront end cap 94 move axially with internal shaft 90, while a frontbushing 93 is held in place within the outer cylinder 89. A number ofcurved clamping blocks 95 extend around a truncoconical surface 96 offront bushing 93, being held inward, against this surface 96, by anelastomeric "O"-ring 97.

The internal shaft 90 is held in the rearward position shown (i.e. inthe direction of arrow 50) by means of a compression spring 98 pressingan adjacent surface of the sliding bushing 91. With internal shaft 90held rearward in this way, inner face 98a of end cap 94 pushes clampingblocks 95 rearward and outward, along truncoconical surface 96. Thismotion of the clamping blocks 95 grasps inner surface 99 of the disk 49,holding the disk in place against a front face 100 of outer cylinder 89.The disk 49 is released by applying a force to piston 92 in a forwarddirection, opposite the direction of arrow 90, to overcome the forceexerted by compression spring 98, so that the internal shaft 50 is movedforward, opposite the direction of arrow 50. This force may be appliedby a number of well known methods, such as through a pneumaticallyoperated push-rod operating on piston 92. The resulting movement of endcap 94 allows the clamping blocks 95 forward and inward, releasing disk49 from the spindle 86.

Referring to FIGS. 5, 7, and 8, pick-and-place mechanism 71 next movesto the rear, in the direction of arrow 50, placing the disk 49 to betextured, which is now at the position indicated by phantom line 83 inFIG. 7, on end cap 94 of spindle 86, with inner shaft 90 held in itsforward position, so that clamping blocks 95 are retracted inward. Next,inner shaft 90 is moved to its rearward position, so that clampingblocks 95 are moved outward, clamping the disk 49 in place, and thegrippers, which have been holding the disk on arm 72, open, releasingthe disk 49. After disk 49 is placed on spindle 86, the pick-and-placemechanism 71 moves forward, opposite the direction of arrow 50, and thespindle drive motor 101 of spindle assembly 88 begins to rotate spindle86 to bring the disk 49 up to a rotational velocity at which exposure tolaser pulses will occur. The spindle assembly 88 also begins to moveinward, in the direction of arrow 102, being driven by a spindletranslation motor 104, carrying the disk 49 into the texturing process.

The laser-texturing station 40 will now be discussed, with specificreferences being made to FIG. 5.

Thus, referring to FIG. 5, within the laser-texturing station 40, a beamfrom an infrared pulsed laser 108 is used to produce the desired surfacetexturing on the disk 49. As described in the co-pending applicationreferenced above, the laser 108 may be, for example, a Nd:YLF solidstate laser, providing an output at a wavelength of 1.047 microns, orNd:YVO₄ solid state laser, operated with a diode pumping signal, drivenfrom a laser diode 110 through a fiber-optic cable 112, and pulsed by aQ-switch control 113. A beam from the laser 108 is directed through anelectronic process shutter 114 and a mechanical safety shutter 116. Whenthe laser-texturing station 40 is operating, a train of laser pulses isemitted from the laser 108, with the actual texturing process beingstarted and stopped by opening and closing the electronic processshutter 114.

The process shutter 114 is actually a mechanical shutter which is openedand held open by the operation of an electromagnet (not shown). Thetermination of the flow of current through the electromagnet causes theprocess shutter to close. The operation of process shutter 114, andhence of the process of texturing an individual disk, is electronicallycontrolled in response to the position of the disk to be textured, asdetermined through the use of a signal generated in response to themovement of, for example, the spindle assembly 88.

The safety shutter 116 remains open during the entire texturing process,unless an error condition, such as a jam of a disk or cassette, occurs.The detection of such an error condition causes the safety shutter 116to close, by means of the software running the laser-texturing tool 37.The laser 108, electronic process shutter 114, and safety shutter 116together form a light-tight assembly, from which even a portion of thelaser beam cannot escape when either shutter 114, 116 is closed.

After passing through the shutters 114, 116, the laser beam enters apolarizing beamsplitter 118, which is oriented so that the portion ofthe laser beam, if any, having an unwanted p-polarization is directeddownwards toward an underlying plate 120, leaving the portion of thelaser beam having a vertical s-polarization to propagate through theremaining optical path. Next, the laser beam passes through a 3×beamexpander/collimator 122, which permits the adjustment of the infraredlaser spot size at a lens entrance.

FIG. 5A is a longitudinal cross-sectional view of the beamexpander/collimator 122. The input beam 122a passes through a diverginglens 122b, which causes the divergence, or expansion, of the beam, andthrough a converging lens 122c, which reduces the divergence of the beamleaving as output beam 122d. The distance between the beam expanderlenses 122b, 122c is manually adjustable through the rotation of athreaded mechanical connection between the lens mounts. In the exampleof the laser-texturing tool 37, this adjustment is made to provide aslightly diverging output beam 122d.

Referring again to FIG. 5, from expander collimator 122, the laser beamis directed by a pair of dielectric-coated steering mirrors 124 to adichroic beamsplitter 126. A visible laser beam, for example from a 2-mWlaser diode 128, is also directed toward the beamsplitter 126,permitting alignment of the optical system by tracing the red laser dot.The infrared beam from laser 108 is made to be coincident with the redbeam from laser diode 128 by manipulating the two steering mirrors 124.About three percent of the laser beam entering beamsplitter 126 from theinfrared laser 108 is reflected from the beamsplitter 126 to a powerdetector 130, which provides in-situ monitoring of the laser power.

The infrared laser beam 131 leaving the dichroic beamsplitter 126 isdirected to a non-polarizing beamsplitter cube 132, which splits thebeam into two beams that are equal in intensity within five percent.These two beams are directed, by means of a pair of steering mirrors134, toward opposite sides of the disk being carried through thetexturing process by spindle assembly 88. After reflection off thesesteering mirrors 134, the laser beams travel as a pair of parallel beams135, separated by a distance of 25 mm, to enter a power control opticsblock 136, in which the intensity of the two beams is balanced bycontrolling the voltage applied to liquid-crystal variable retarders. Inthis way the intensity of the parallel laser beams leaving the powercontrol optics block 136 is made equal within one percent.

FIG. 5B is a partially sectional plan view of the beamsplitter cube 132,together with steering mirrors 134 and the power control optics block136. The two laser beams 135 forming inputs to the block 136 extendparallel to, and equally offset from, an axis 136a of the power controloptics block 136, about which the various elements of this block 136 aresymmetrically deployed. Symmetrical beams 135 result from the fact thatthe input beam 131 to the beamsplitter cube 132 is directed at a45-degree angle with respect to the optics block axis 136a, with thereflective surface 132a within the beamsplitter cube being aligned alongthe optics block axis 136a. Each of the steering mirrors 134 is alignedto be struck by an associated beam from the beamsplitter cube 132 at anangle of incidence of 67.5 degrees.

Referring to FIG. 5B, adjustments for bringing the separate laser beams135 into a parallel condition, and for otherwise aligning them, areprovided by several manually turned knobs. Beamsplitter cube 132 ismounted on a rotary stage 132b, with a pair of knobs 132c tilting thecube 132 about orthogonal axes, and with a knob 132d providing for therotation of the cube 132. For example, a rotary stage suitable for thisapplication is supplied by the Newport Corporation of Irvine, Calif.,under their part number P032N. Each steering mirror 134 is mounted by anadjustable mirror mount 134a, which includes a pair of knobs 134b usedto tilt the associated mirror 134 about mutually perpendicular axes.Mirror mounts suitable for this application are supplied, for example bythe Ealing Electro Optics, Inc. Holliston, Mass., under their catalognumber 37-4777.

Within the power control optics block 136, the power of the two beams135 from beamsplitter cube 132 is balanced, so that these beams havepower levels within one percent of one another. The beamsplitter cube132 splits the single beam arriving from the laser into a pair of beams135 having power levels within five percent of one another. While thebeamsplitter cube 132 is a non-polarizing device, the laser beams 135entering the power control optics block 136 are nominally, orpredominately, s-polarized, having passed through polarizingbeamsplitter 118 (shown in FIG. 5).

Within the power control optics block 136, each of these beams 135 firstenters a liquid crystal variable retarder 136b. Each of these retarders136b includes a cavity 136c formed between a pair of fused silicawindows 136d spaced a few microns apart. The interior surface of eachwindow 136d has a transparent conductive indium tin oxide coating. Thecavity 136c is filled with birefringent nematic liquid crystal materialwith molecules that tip according to a voltage applied between thetransparent conductive coatings of the windows 136c. The angle ofpolarization of the laser beam 135 entering each retarder 136b ischanged according to the voltage applied across the cavity 136c by meansof the coatings on windows 136d. Thus, the s-polarization of each beam135 entering a retarder 136b is altered, in a continuously variablemanner, toward a p-polarization of the beam 136e leaving the retarder136b. A suitable liquid crystal variable retarder may be obtained, forexample, from Meadowlark Optics, of Longmont, Co., under their partnumber LVR-100-1047-V.

The voltage signal driving each liquid crystal variable retarder 136b isprovided by the output of a function generator 137, which preferablyproduces a DC-balanced 2kHz square wave having an amplitude which isadjustable to determine how the polarization of the beam passing throughthe retarder 136b is altered.

After exiting the retarder 136b, each beam 136e enters a polarizingbeamsplitter 136f, which reflects s-polarized power inward to a beamdump 136g to be dissipated within a cavity 136h, while transmittingp-polarized energy to an non-polarizing beamsplitter 136i. Eachnon-polarizing beamsplitter 136i reflects about one percent of theenergy incident upon it upward, providing the input to a power detector136j. The remaining energy is transmitted through a quarter-wave plate136k, which converts the p-polarized energy incident upon it into acircularly-polarized beam 136m exiting the power control optics block136.

Referring to FIGS. 5 and 5B, independent means to measure and controlthe power levels of the single beam 135 derived from the output of laser108 and of each of the beams 136m exiting the power control optics block136 are provided. The power level of the single beam 131, which ismeasured by monitoring the output of power detector 130, is controlled,or attenuated, by varying an input signal to laser 108. The combinationof a retarder 136b with a polarizing beamsplitter 136f provides aconvenient way to control the power level of each beam 136m exiting theblock 136, while the combination of a non-polarizing beamsplitter 136iwith a power detector 136j provides a convenient means for measuringthis power level. The output signals from power detectors 130, 136j areindividually calibrated using measurements of beams 136m at the exit ofthe power control optics block, or farther along the optical path towardthe point at which a disk 49 is textured. This type of calibration isgenerally needed because of a number of factors, such as differences inthe percentage of incident power reflected within the beamsplitters 126,136i aiming beams at these power detectors. The outputs of powerdetectors 130, 136j are preferably displayed externally on the lasertexturing tool 37 (shown in FIG. 4).

A method for manually setting-up or readjusting the various laser powerlevels includes the steps of monitoring the outputs of power detector130 and making corresponding adjustments to a signal driving the laser108. The two beams 136m are balanced by observing the outputs of bothpower detectors 136j with both retarders 136b set to transmit maximumlevels of p-polarized power, and by reducing the level of p-polarizedpower transmitted by the retarder corresponding to the higher powerlevel read by one of the power detectors 136j, until these two detectorsindicate the same power level, with calibration factors beingconsidered. As the level of p-polarized power is decreased in either ofthe beams, the level of power present in the corresponding output beam136m is decreased, as the increased s-polarized power is rejected inwardby the polarizing beam splitter 136f. In this way, the output levels ofthe two beams are balanced by attenuating the beam initially having thehigher level.

In the example of FIG. 5, the parallel laser beams 136m from powercontrol optics block 136 are reflected off a right shuttling mirror 138,being directed toward a disk carried through the texturing process fromthe right disk-handling station 38.

FIG. 5C is a plan view of the optical devices associated with the rightdisk-handling station 38. For example, each of these beams 136m passesthrough a focussing achromatic triplet lens 140, having a focal lengthof 25 mm, and is reflected toward the surface of the disk 49 beingtextured by a right-angle prism 142.

Referring to FIG. 5C, each lens 140 is mounted in a finely adjustablemanner, permitting the adjustments needed to center the beam and toachieve optimum focus on each side of the disk 49. A first stage 140a,moved by a first micrometer-type screw mechanism 140b allows a lensfocussing adjustment in the directions of arrow 140c. A second stage140d, moved by a second screw mechanism 140e, allows lateral movement ofthe lens 140, in the directions indicated by arrow 140f. A third stage140g, in which the lens 140 is mounted, allow vertical movement throughthe rotation of a third mechanism 140h.

Each prism 142 is slightly tilted, so that a laser beam reflected offthe surface of the disk being textured is not transmitted back throughthe optical path, being instead generally reflected outward as areflected beam 142a. Each prism 142 is mounted on a pivot arm 142b,pivotally mounted by a pin 142c to a stage 142d, which is in turn movedin the directions of arrow 140f by a micrometer-type screw mechanism142e. The pivotal movement of each pivot arm 142b may be used to set thepoint on the disk 49 at which texturing begins. This type of adjustmentis particularly useful for adjusting the process to produce texturedsurfaces on each side of the disk 49, starting and ending at the samediameters on the disk. When this is done, since the pivot pin 142c isoffset from the reflective surface of the prism 142, the laser beam isexpected to move along this reflective surface. If this movementdisplaces the laser beam too far from the center of this reflectivesurface, the position of prism 142 is corrected with screw mechanism142e.

Referring again to FIGS. 5 and 5A, and continuing to refer to FIG. 5C,beam expander 122 is adjusted by changing the distance between 122b andlens 122c, during the initial adjustment of this apparatus, so that thelaser beam 122a entering the beam expander 122 at a diameter of about0.5 mm leaves the beam expander 122 as beam 122d with a diameter ofabout 1.3 mm, and so that the beam entering a focussing lens 140 has adiameter of about 1.5 mm. This lens 140 is focussed by movement in thedirection of arrow 140c, using the screw mechanism 140b, so that thelaser beam has a diameter of about 20 microns at the surface of a disk49 being textured. An independent adjustment of this kind is made tofocus a beam on each side of the disk 49.

Further adjustments of the beam expander 122 and of each focussing lens140 may be made to effect changes in the process and in the texturedspots generated on the disk 49. In general, adjusting the beam expander122 to increase the diameter of the laser beam striking each focussinglens 140 makes it possible to focus a smaller beam diameter on the disk49.

Referring to FIGS. 5, 5B, and 5C, despite the precaution of tilting eachprism 142, to prevent the return of laser power reflected off the disk49 within the optical path, some such power can be expected to return,due particularly to reflection from the non-uniform disk surfaceproduced by the texturing process. However, the s-polarized lightreflected back along the optical paths in this way is rejected by eachpolarizing beamsplitter 136f in the power control optics block 136,being directed outward as a beam 136n.

The movement of a disk through the laser-texturing process, and itssubsequent return to the cassette from which it has been taken, will nowbe discussed, with particular reference being made to FIGS. 5 and 7.

Thus, referring to FIGS. 5 and 7, the disk 49 clamped to spindle 86 isfirst brought up to the rotational speed desired for the texturingprocess, as the motion of spindle assembly 88 drives the disk 49 inward,in the direction of arrow 102, to or past the point at which the innerdiameter, indicated on FIG. 7 by phantom line 146, of the surfaces to betextured is adjacent to the point at which exposure will occur to laserbeams reflected from prisms 142. The actual exposure, which is startedby opening electronic process shutter 114, occurs as the disk 49 isrotated, for example, at a constant speed, by spindle drive motor 101and as the disk 49 is moved in the outward direction, opposite arrow102, for example, at a constant speed, by the spindle translation motor104. When the disk 49 passes the point at which the outer diameter,indicated by phantom line 148, of the surfaces to be textured isadjacent to the point at which exposure occurs to laser beams reflectedfrom prisms 142, electronic process shutter 114 is closed to terminatethe exposure of the surfaces of disk 49 to the laser beam. Thus, anannular space on disk 49 is textured by placing a number oflaser-generated texture patterns along a spiral, with the distancebetween the patterns adjacent along the spiral being determined by therate at which laser 108 is pulsed, and by the rate of rotation ofspindle 86, while the distance between radially adjacent segments of thespiral is determined by the rates of rotation and translation of spindle86.

After completion of the texturing process, the rotation of spindle 86 isstopped, or allowed to decelerate, as the spindle assembly 88 continuesmoving outwardly, opposite arrow 102, to stop in the position adjacentto grippers 78, at the inward-extending end of the arm 72. At thispoint, the arm 72 is held forward, in the direction opposite arrow 50,so that the disk 49 can pass behind the grippers 78, which are heldopen. When this outward motion of spindle assembly 88 is complete, andwhen the rotational motion of spindle 86 is fully stopped, the arm 72 ismoved rearward, and the grippers are closed to engage the disk 49. Next,the shaft 90 (shown in FIG. 8) is moved forward so that the clampingblocks 95 (also shown in FIG. 8) are retracted inward, releasing thedisk 49 from spindle 86. Then, the arm 72 is moved forward, opposite thedirection of arrow 50, and arm 72 is rotated 180 degrees about the axisof its drive shaft 73, opposite the direction of arrow 74, and the arm72 is moved rearward, in the direction of arrow 50, moving the disk 49,which has most recently been textured, into position above the disklifter 59. Next, lifter 59 moves upward, accepting the textured disk inits groove 84. The grippers on arm 72 holding the textured disk areopened, and the lifter 59 then descends, placing the textured disk 49 ina pocket 51 within the cassette 58.

The preceding discussion has described the movement of a single disk 49from the cassette 58, in right disk-handling station 38, through thetexturing process in laser-texturing station 40, and back into thecassette 58. In a preferred version of the present invention, two disksare simultaneously moved in opposite directions between the cassette 58and the spindle 86, which carries each disk through the texturingprocess. This type of disk movement will now be described, withparticular references being made to FIGS. 5 and 7.

Referring to FIGS. 5 and 7, except during the movement of the first andlast disks 49 held within an individual cassette 58, each rotationalmovement of arm 72 in or opposite the direction of arrow 74 preferablycarries one disk 49 from the disk lifter 59 to spindle 86 withingrippers 77, while another disk 49 is simultaneously carried withingrippers 78 from the spindle 86 to disk lifter 59. Sequential rotationalmovements of arm 72, which are similar in their movement of disks, occurin opposite rotational directions to avoid the winding of air hoses toactuators 79 and of wires to grippers 77, 78, which would occur if suchmovements were to continue in one direction.

Furthermore, a preferred version of the present invention returns eachtextured disk 49 to the cassette pocket 51 from which it has been taken,leaving the pockets 51 which have been determined to be empty byproximity sensor 70a in an empty condition. These conditions areachieved in a preferred version of the present invention, by allowingthe simultaneous movement of two disks 49 by the pick and placemechanism 71, and by using the indexing conveyor 57 to return cassette58 to the position in which disk lifter 59 accesses the pocket fromwhich a disk 49 was taken before replacing the disk 49 in the cassette58.

As a disk 49, which is hereinafter called the "A" disk 49 forconvenience, is being taken through the texturing process by spindle 86,a "B" disk 49, which is the next disk 49 in the direction opposite arrow50 past the cassette pocket 51 from which the "A" disk 49 has beentaken, is found by movement of the cassette 58 in the direction of arrow50 past the proximity sensor 70a. At this point, the movement ofcassette 58 is stopped, and disk lifter 59 moves the "B" disk 49 upward,into the position indicated by phantom line 82. When the process oftexturing the "A" disk 49 is finished, spindle 86 moves the "A" disk 49into the position indicated by phantom line 83. When both the "A" and"B" disks 49 have been positioned in this way, pick-and-place mechanism71 moves to the rear, in the direction of arrow 50, and both sets ofgrippers 77, 78 are closed to grasp the "A" and "B" disks 49. Within thespindle 86, shaft 90 (shown in FIG. 8) is moved to the front, movingclamping blocks 95 inward to disengage the spindle from the "A" disk 49,and the disk lifter 59 moves downward to disengage from the "B" disk 49.Next, the pick-and-place mechanism 71 moves forward, opposite thedirection of arrow 50, and the arm rotational drive motor 75 drives arm72 through a 180-degree angle in the direction of arrow 74. Now, thepositions of the "A" and "B" disks 49 are reversed, with the "A" disk 49being positioned for movement through the texturing process on spindle86, and with the "B" disk 49 being positioned for return to cassette 58.Next, pick-and-place mechanism 71 moves to the rear, in the direction ofarrow 50, placing the "B" disk 49 on spindle 86, and aligning the "A"disk 49 with disk lifter 59.

Thus, a first disk transfer point is established at the disk locationshown by phantom line 82, and a second disk transfer point isestablished at the disk location shown by phantom line 83, both withpick-and-place mechanism 71 moved to the rear, in the direction of arrow50. At the first disk transfer point, a disk 49 is transferred in eitherdirection between pick-and-place mechanism 71 and disk lifter 59. At thesecond disk transfer point, a disk 49 is transferred in either directionbetween pick-and-place mechanism 71 and spindle 86.

In a preferred mode of operation, computing system 70 stores dataindicating the pocket 51 within cassette 58 from which each disk istaken. This data is subsequently used to determine how the cassette 58is moved opposite the direction of arrow 50 to return to the place fromwhich the "A" disk 49 has been taken. When a cassette full of disks tobe textured has been loaded into the disk-handling station 38, thecassette is moved one pocket position in the direction opposite that ofarrow 50, from the position in which the pocket at which "B" disk 49 hasbeen taken is directly above disk lifter 59, to the position in whichthe pocket at which "A" disk 49 has been taken is above disk lifter 59.If the cassette 58 was not full of disks 49 to be textured when it wasloaded into disk-handling station 48, the cassette 58 may have to bemoved farther than one pocket position opposite the direction of arrow50. In any case, the cassette is moved so that the pocket from which the"A" disk 49 was taken is above disk lifter 59, using disk position datastored within computing system 70 and moving the cassette using indexingconveyor 57. This cassette movement can occur as the "A" disk is beingmoved, by pick-and-place mechanism 71, into place for reinsertion intothe cassette 58, with the pick-and-place mechanism 71 moved forward,opposite the direction of arrow 50.

Next, disk lifter 59 moves upward, engaging "A" disk 49 within itsgroove 84, and the shaft 90 (shown in FIG. 8) is moved rearward, in thedirection of arrow 50, so that clamping blocks 95 are extended outwardto hold "B" disk 49 (also shown in FIG. 8) on the spindle 86. Thegrippers holding the "A" disk are opened, and disk lifter 59 movesdownward, restoring "A" disk 49 into the pocket 51 from which it wastaken, and spindle 86 moves inward, in the direction of arrow 102, whilerotationally accelerating the disk to the rotational velocity at whichtexturing will occur. In this way, preparations are made to texture thenext disk 49, which is, at this time, the "B" disk.

The first disk 49 taken from each individual cassette 58 is moved alonefrom disk lifter 59 to spindle 86, without the simultaneous movement ofanother disk 49 in the opposite direction, since there is no other diskavailable for such movement. Similarly, the last disk 49 taken from eachindividual cassette 58 is moved alone from spindle 86 to disk lifter 59,since there is no other disk available for movement in the oppositedirection. The determination that the last disk 49 to be textured hasbeen removed from the cassette 58 is made when the last pocket 51 intowhich disks 49 can be placed is moved past disk lifter 59 without thedetection of another disk 49 by proximity sensor 70a. Only a singlecassette 58 at a time is moved onto indexing conveyor 57, with all ofthe disks 49 to be textured within the cassette 58 being removed fromthe cassette 58, sent through the texturing process, and returned to thecassette 58 before any of the disks 49 in the next cassette 58 are soprocessed.

FIG. 9 is a cross-sectional plan view of a slider mechanism 149 used tomove a transfer table 150 on which cassettes are transferred fromindexing conveyor 57 to output conveyor 61, taken as indicated bysection lines IF--IF in FIG. 6.

Referring to FIGS. 6 and 9, the transfer table 150 is mounted atopslider mechanism 149, including a slider 151, having a pair of cylinders152, through which a pair of hollow shafts 153, 154 extend. The shafts153, 154 are in turn mounted to extend between end blocks 155. Theslider 151 is slidably mounted on the shafts 153, 154 by means ofbearing assemblies 156, which also include air-tight seals preventingthe outward flow of air from the ends of cylinders 152. A central piston157 is also attached to slide with the slider 151 along each shaft 153,154. Each piston 157 includes seals separating the cylinder 152, withinwhich it is attached, into an inward chamber 158 and an outward chamber159, each of which is alternately filled with compressed air orexhausted to effect movement of the slider 151.

To move slider 151 inward, in the direction of arrow 102, compressed airis directed to the inward chambers 158, from hose 160, through a hole161 in shaft 153. As this occurs, air is exhausted from outward chambers159, through a hole 162 in shaft 154, and through hose 163. Both inwardchambers 158 are connected by an inward transverse hole 164, and bothoutward chambers 159 are connected by an outward transverse hole 165.Thus, as compressed air is directed through hose 160 while hose 163 isexhausted to the atmosphere, the resulting expansion of inward chambers158, together with a contraction of outward chambers 159, moves slider151 inward, in the direction of arrow 102, aligning transfer tableconveyor 60 with indexing conveyor 57.

Similarly, to move slider 151 outward, opposite the direction of arrow102, compressed air is directed to the outward chambers 159, from hose163, through hole 162 in shaft 154. As this occurs, air is exhaustedfrom inward chambers 158, through hole 161 in shaft 153, and throughhose 160. Thus, as compressed air is directed through hose 163 whilehose 160 is exhausted to the atmosphere, the resulting expansion ofoutward chambers 159, together with a contraction of inward chambers158, moves slider 151 outward, opposite the direction of arrow 102,aligning transfer table conveyor 60 with output conveyor 61.

The movement of a cassette 58 following the return thereto of all disks49, having been textured, will now be discussed, with specificreferences being made to FIGS. 5, and 6.

Thus, referring to FIGS. 5 and 6, when it is determined that the lastdisk 49 to be textured in a cassette 58 has been processed and returnedto the cassette 58, both intermediate conveyor 57 and transfer tableconveyor 60 are turned on to move the cassette 58 rearward, in thedirection of arrow 50, until the cassette 58 is completely on transfertable conveyor 60, as indicated by the output of transfer table cassettesensor 69. Upon the indication of sensor 69, movement of conveyors 57and 60 is stopped, and a slider mechanism 149 is operated to drive thetransfer table 150, which includes transfer table conveyor 60, in anoutward direction, opposite the direction of arrow 102 along hollowshafts 153, 154. After this motion is stopped with transfer tableconveyor 60 in alignment with output conveyor 61, the conveyors 60, 61are turned on to move cassette 58 to the front, opposite the directionof arrow 50. If other cassettes are not stored along the output conveyor61, this movement is stopped when the cassette has been brought to thefront of the conveyor 61, to the position in which cassette 166 is shownin FIG. 5, as indicated by a first output cassette sensor 168. At thispoint, the cassette 166, with processed disks 49, is ready for removalfrom the disk texturing tool 37.

Continuing to refer to FIG. 5, while this condition of readiness ispreferably communicated to the system operator through a visible oraudible indication, the removal of a cassette 166 with textured disks 49is not generally required to permit continued operation of the disktexturing tool 37. Space is provided along output conveyor 61 for thestorage of a number of cassettes 166 filled with textured disks 49. In afirst version of this output system, all such cassettes 166 are storedalong the surface of output conveyor 61. In a second version of thisoutput system, the first cassette to reach the front of output conveyor61 is stored on a raised platform

The operation of the first version of this output system will now bedescribed. In this version, if a cassette 166 is waiting for removal atthe front of output conveyor 61 when the processing of disks 49 withinanother cassette 58 is completed, output conveyor 61 is turned on tomove the cassette 166 rearward, in the direction of arrow 50. Thismovement is stopped when the presence of cassette 166 is detected by asecond output cassette sensor 170. Then, with transfer table conveyor 60in alignment with output conveyor 61, both transfer table conveyor 60and output conveyor 61 are turned on to move cassettes 166 and 58together to the front of conveyor 61, where this motion is stopped asfirst output cassette sensor 168 detects the presence of cassette 166.If necessary, this process is repeated several times, until outputconveyor 61 is filled with a queue of cassettes holding disks 49 whichhave completed the texturing process. In each case, the rearward motionof output conveyor 61, in the direction of arrow 50, is stopped when therearmost cassette in the queue reaches second output cassette sensor170, and the subsequent forward motion of output conveyor 61 is stoppedwhen the forwardmost cassette in the queue reaches first output cassettesensor 168.

The operation of the second version of this output system will now bedescribed. This version requires an additional cassette lifting platform172, which is similar to the platform 54 used with input conveyor 47,and a third output cassette sensor 174. With this version, the firstcassette 166 to reach the end of output conveyor 61 is raised off theconveyor with lifting platform 172, to remain in a raised position untilit is removed by the tool operator. With a cassette 166 in the raisedposition, output conveyor 61 is operated in both directions while notaffecting the position of the cassette 166. Thus, when a secondcassette, such as cassette 58, is loaded onto output conveyor 61, thisconveyor 61 is turned on to drive the cassette forward, in the directionopposite arrow 50. This motion is stopped when the cassette is detectedby third output cassette sensor 174. When the disks in a third cassetteare completed, output conveyor 61 is turned on to drive the secondcassette rearward. This motion is stopped when the second cassette isdetected by second output cassette sensor 170. Then both transfer tableconveyor 60 and output conveyor 61 are turned on to move the second andthird cassettes forward, opposite the direction of arrow 50, until thesecond cassette is detected by third output cassette sensor 174.

Again, this process is repeated until output conveyor 61 is filled witha queue of cassettes holding disks 49 which have completed the texturingprocess. In each case, the rearward motion of output conveyor 61, in thedirection of arrow 50, is stopped when the rearmost cassette in thequeue reaches second output cassette sensor 170, and the subsequentforward motion of output conveyor 61 is stopped when the forwardmostcassette in the queue reaches third output cassette sensor 174. Thesemovements occur as the first cassette 166 remains on raised platform172.

At any point, if the cassette 166 on platform 172 is removed by the tooloperator with one or more cassettes remaining on output conveyor 61, theconveyor 61 is turned on to drive the next cassette to the end of theconveyor 61, as detected by first output cassette sensor 168. Theplatform 172 is again raised to lift this cassette off output conveyor61.

The methods described above for handling cassettes provide theparticular advantage of not operating any conveyor system 47, 57, 60, 61in sliding contact with a cassette. The generation of wear particlesfrom relative motion between conveyor systems and cassettes is thereforeavoided. Such wear particles could otherwise contaminate themanufacturing process of which this texturing is a part. Furthermore,the useful life of conveyor belts and cassettes is increased, withcassettes and conveyer belts being likely to last as long as variousother moving parts of the disk texturing tool 37.

The configuration of output conveyor 61 extending alongside inputconveyor 47 provides the advantage of bringing output cassettes, holdingdisks which have gone through the texturing process, back to a placeadjacent to the place where input cassettes are loaded. This facilitatesservicing the tool 37 by personnel who must both load and unloadcassettes. Furthermore, additional space for queuing cassettes along theconveyors is gained without having to increase the length of the tool 37along the conveyors.

The preceding discussion of the movement of cassettes and disks hasfocussed on such movement within right disk-handling station 38 of thelaser-texturing tool 37. Thus, the various movements of disks andcassettes described above are used alone if the left disk-handlingstation 39 is not available. For example, the left disk-handling stationmay not be available due to a technical problem, or simply becausecassettes have not been loaded into it. Furthermore, an embodiment ofthe present invention has only a single disk-handling tool, which isoperated as described in detail above. Nevertheless, in the preferredmethod of operation of the preferred embodiment of the presentinvention, which will now be described with particular reference beingmade to FIG. 5, both right disk-handling station 38 and leftdisk-handling station 39 are used in an alternating fashion to presentdisks to be textured within laser-texturing station 40.

Thus, referring to FIG. 5, in a preferred version of the presentinvention, the operation of left disk-handling station 39 is generallythe same as operation of right disk-handling station 38, with variouselements of the apparatus within the left disk-handling station 39 beingmirror image configurations of corresponding elements within the rightdisk-handling station 38. The preceding discussion of operations withinright disk-handling station 38 is equally applicable to operationswithin left disk-handling station 39, with rearward motions, in thedirection of arrow 50, remaining the same, and with inward motions, inthe direction of arrow 102 continuing to be directed toward the centerof the laser texturing tool 37, in the direction of arrow 166, withinleft disk-handling station 39. Similarly, forward motions, opposite thedirection of arrow 50 are in the same direction in both left and rightdisk-handling stations 38, 39, while outward motions in leftdisk-handling station 39 are opposite the direction of arrow 166.

Within disk-texturing station 40, right shuttling mirror 138 is mountedon a mirror slide 176, together with a left shuttling mirror 178. Mirrorslide 176 is operated pneumatically, sliding on a pair of shafts 180,using a mechanism operating generally as described above in reference toFIG. 9. With mirror slide 176 in its leftward position, moved in thedirection of arrow 181 as shown in FIG. 5, the laser beams passingthrough power control optics block 136, having been derived from theoutput of infrared laser 108, are directed to disk 49, clamped onspindle 86 of right disk-handling station 39, as previously described.Mirror slide 176 is alternately moved into a rightward position, so thatthe laser beams passing through power control optics block 136 reflectoff left shuttling mirror 178, being directed to a disk 182 held byspindle 184 of left disk-handling station 39. In this way, the laserbeams employed in the disk texturing process are directed to eitherdisks within the right disk-handling station 38 or left disk-handlingstation 39 simply by moving mirror slider 176.

While the above discussion describes the use of a sliding mechanismhaving two mirrors to direct the laser beams between the twodisk-handling stations 38, 39, a single pivoting mirror couldalternately be used for this purpose.

The operation of right disk-handling station 38, which has beendescribed in some detail above, may be considered to consist basicallyof disk-movement cycles alternating with texturing cycles, wherein eachdisk movement cycle consists of the movement of one or two disks bypick-and-place mechanism 71, and wherein each texturing cycle consistsof the movement of a single disk on the spindle 86. Whenever sufficientdisks are available for texturing to allow the disk texturing tool 37 tooperate at full capacity, each disk-movement cycle of rightdisk-handling station 38 occurs simultaneously with a texturing cycle ofleft disk-handling station 39, and each disk-movement cycle of leftdisk-handling station 39 occurs simultaneously with a texturing cycle ofright disk-handling station 38. In this way, the use of the texturingprocess available through operation of infrared laser 108 is maximized,along with the overall process speed of the laser texturing tool 37.However, when disks to be textured are not available from one of thedisk-handling stations 38, 39, the other disk handling station cancontinue to run at its full speed.

Referring to FIGS. 5-7, a preferred version of the present inventionincludes a bar code scanner 186 for reading bar code labels (not shown)placed on a side of a cassette 48, which is put on platform 54. To usethis feature, the computing unit 70 executes a program relating barcodes read by scanner 186. Data gathered by reading bar code labels maybe stored and used by an inventory control system to keep track of workin process.

The present invention provides advantages of optimized productivity andflexibility. In a preferred mode of operation, both disk-handlingstations 38, 39 are simultaneously used as described above, maximizingthe rate of production for the laser texturing tool 37. The use of laser108 is optimized, with various disk-handling processes in eachdisk-handling station 38, 39 occurring while a disk 49, 172 in the otherdisk-handling station is being exposed to the laser. The use of separatedisk-handling stations also provides flexibility; if either of thedisk-handling stations 38, 39 is disabled, production can continue at areduced rate using the other disk-handling station. A singledisk-handling station 38, 39 can also be used, if desired, whenuntextured disks sufficient for the use of both stations are notavailable for the process.

Referring again to FIGS. 5 and 5B, the preceding discussion hasdescribed a method for texturing disks using a laser beam system whichhas been manually adjusted to provide a certain overall power at asingle beam 135 and for balancing the two beams 136m resulting fromsplitting the single beam 135. The laser beam system may alternately beset up by providing more laser power than necessary in the single beam135 and by subsequently adjusting each beam 136m to a level defined by aset point, so that each beam 136m is attenuated during the adjustmentprocess by the corresponding liquid crystal variable retarder 136b.

Furthermore, a preferred version of the present invention includesautomatic means for initially making the laser power adjustments and formaintaining these adjustments.

FIG. 10 is a block diagram of a subsystem 200 for adjusting andmaintaining the power in a laser single beam 136m at a set-point level.Referring to FIGS. 5B and 10, inputs to the subsystem 200 are providedby the outputs of a laser power detectors 136j, which have previouslybeen discussed in reference to FIG. 5B, each of which measures the powerof a single beam 136m. The output of each detector 136j is fed into ananalog to digital convertor 202, and the outputs of the two convertors202 are individually provided as 12-bit inputs to ports of amicrocontroller 206. Program and data information is stored in a randomaccess memory 207 of the microcontroller 206. Operator inputs to themicrocontroller 206 are provided through a keypad 208, while programinformation is typically loaded into the microcontroller 206 through amagnetic diskette 209. A display unit 210 is also connected to receiveoutputs from the microcontroller 206. Two output ports of the microcontroller 206 are individually connected to digital to analogconvertors 212. The output of each digital to analog convertor 212drives an input of a function generator 137, which in turn produces a2KHz square wave function having a voltage determined by the outputvoltage of the attached digital to analog convertor 212. As previouslydescribed in reference to FIG. 5B, each function generator 137 drives aliquid crystal variable retarder 136b, which variably attenuates thepower level of an associated laser beam 136m.

FIG. 11 is a flow diagram of a program executing in the microcontroller206. This program can operate in a teach mode, a set point mode, amonitor mode, or a run mode. The system operator determines the mode inwhich the system is placed, indicating his choice by means of the keypad208 (shown in FIG. 10). Each mode is entered from a start point in block218.

Referring to FIGS. 5B, 10, and 11, in the teach mode, which is enteredwith an affirmative determination in block 220, the microcontroller 206reads the power of a laser beam 136m while stepping the voltage drivingthe function generator 137, which in turn drives the liquid crystalvariable retarder 136b associated with the laser beam 136m beingmeasured. In the first segment of the teach mode, several initializationfunctions are performed, with a teach mode screen being sent to thedisplay 210 in block 222, with a counter being reset to zero in block224, and with the output voltage level to the function generator 137being set to an initial value of 2.33 mv in block 226.

Next, a program loop is entered, with a 30 ms (millisecond) delay inblock 228 providing time for the retarder 136b to stabilize before thelaser power is read in block 230 and stored in a table within memory207. Next, in block 232, the voltage driving the function generator 137is increased by the incremental value of 2.33 volts. Then, in block 236,a determination is made of whether the counter value has reached 4096.This exemplary value represents a pre-determined level at which theteach mode is determined to be completed. If this value has not beenreached, the system returns to block 228, to repeat the process ofmeasuring a laser power level and incrementally increasing the drivevoltage level. Each time this occurs, the measured drive voltage anddrive power level associated therewith are stored as correspondingvalues of a look-up table being built in memory 207.

After the end of the teach mode has been reached, as determined in block236, a further determination is made in block 238 of whether theoperator has chosen to display a graph of power versus driving voltage.If the operator has chosen this display, as indicated by an affirmativedetermination in block 238, such a graph is displayed on the displayunit 210 in block 240. In either case, after the completion of the teachmode, the system returns to the start point 218.

In the set point mode, which is entered with an affirmativedetermination in decision block 242, the operator can enter the valuedesired for a laser power set point through the key-pad 208. Thecontroller then determines the drive voltage associated with this powerlevel from the look-up table stored in memory 207. The 12-bit codeassociated with this drive voltage is then sent to the correspondingdigital to analog convertor 212. The operator can perform this routineas often as needed, until the system is properly set up.

Thus, the set point mode is started in block 244, as a screen for thismode is shown on display unit 210. The system then waits, going througha loop from decision block 246, for the operator to enter a set pointvalue. When such a value has been entered, the system, in block 248,finds the drive voltage associated with this set point value. In block250, this drive voltage is applied to the function generator 137. Inblock 252, the power of the corresponding laser beam 136m is read, to bedisplayed through the display unit 210 in block 254. The system thenreturns to start point 218.

The monitor mode is used to determine variations in the output power oflaser 108 (shown in FIG. 5) with time. Thus, after the monitor mode isentered, as determined by an affirmative determination in block 256, atimer is started in block 258. A laser power level is read in block 260and stored in a power table along with the time, from the timer, atwhich it is produced. Until a pre-set time out time value is reached, asindicated by an affirmative determination in block 262 the measurementand storage functions of block 260 are repeated on a periodic basis.When this time out condition has been reached, the timer is stopped inblock 264. Next, a determination is made in block 266 of whether theoperator has indicated, using the keypad 208, that a graph showing thevariation of laser power with time is to be displayed. Thus, anaffirmative determination in block 266 results in the display of such agraph on display unit 210 in block 268.

Normal operation of the laser texturing tool 37 (shown in FIG. 4) isaccomplished in the run mode. When the run mode is selected, asindicated by an negative determination in block 256, since the otherpossible modes have been eliminated at this point, the system is lockedto a laser power set point previously determined through operation inthe set point mode. Changes are made in the drive voltage into thefunction generator 137 so that the corresponding laser beam 136m is heldnear the set point power, as measured by the corresponding powerdetector 136j. If the laser beam power is outside predetermined limitingvalues, an alarm is sounded, and the tool 37 is placed in a paused mode.

In the run mode, the system first determines, in block 272, whether theprocess shutter 114 (shown in FIG. 5) is closed. If it is closed, no newdata can be derived, so the system returns to start point 218 withoutchanging the set point. If the shutter is not closed, as indicated by anegative determination in block 272, the function generator 137 isdriven in block 274 with a drive voltage determined by themicrocontroller 206 to correct the laser power measured on a previouspass through this routine to the set point value. (On the first pass, aset point voltage as determined in the set point mode is used for thispurpose). Next, in block 276, the actual laser power is read. Tocontinue running the system, the laser power must be withinpre-determined limits.

If this power is too high, as determined in block 278, or too low, asdetermined in block 280, an alarm is sounded in block 281, the powerreading and set point are displayed on display unit 210 in block 282,and the laser texturing tool 37 (shown in FIG. 4) is placed in pausemode in block 284. From this point, the system waits for the operator topress a reset switch, as determined in block 286, before stopping thealarm. Even if the alarm is stopped, production remains halted untilcorrections are made by the operator, who then takes the system out ofpause mode.

If the laser power is within the pre-set limits, the system continues,repeatedly going through a loop including the run mode sequences andreturning to the start point 218 as, within limits, excursions in laserpower are corrected by changes in the voltage driving the functiongenerator 137.

The preceding discussion in reference to FIG. 11 has covered a situationin which a program is used to control the power within a single laserbeam 136m. In reality there are two such beams 136m to be controlledduring the laser texturing process. It is therefore understood thatprocessor 206 is operating as a multitasking processor running theprogram discussed in reference to FIG. 11 for each of these two laserbeams 136, with data supplied through the two analog to digitalconvertors 202 and supplying data to the two digital to analogconvertors 212.

While the invention has been described in its preferred form orembodiment with some degree of particularity, it is understood that thisdescription has been given only by way of example and that numerouschanges in the details of construction, fabrication and use, includingthe combination and arrangement of parts, may be made without departingfrom the spirit and scope of the invention.

What is claimed is:
 1. Apparatus for directing portions of a laser beamsimultaneously at opposite sides of a first disk being textured bypulses from said laser beam, wherein said apparatus comprises:a firstbeamsplitter dividing said laser beam into transmitted and reflectedbeams; first beam directing means for directing said transmitted beamalong a first optical path and for directing said reflected beam along asecond optical path; attenuation means disposed along each said opticalpath for controlling an output power level of an output beam directedtherefrom; power detection means disposed along each said optical pathfor measuring said output power level, and second beam directing meansfor directing a first output beam along said first optical path to afirst side of said first disk and for directing a second output beamalong said second optical path to a second side of said first disk,opposite said first side thereof.
 2. The apparatus of claim 1, whereineach said attenuation means comprises:a variable retarder changing anangle of polarization of a polarized laser beam transmitted therethroughin accordance with an input voltage applied to said variable retarder; apolarizing beamsplitter receiving an input beam in said first directionalong said optical path from said variable retarder, wherein saidpolarizing beamsplitter transmits a first portion of said input beam,having a first polarity, along said optical path, and wherein saidpolarizing beamsplitter reflects a second portion of said input beam,having a polarity perpendicular to said first polarity, away from saidoptical path.
 3. The apparatus of claim 2:wherein said apparatusadditionally comprises a quarter-wave-length plate disposed along eachsaid optical path; and wherein a laser beam reflected back from saidfirst disk is reflected away from said optical path by said polarizingbeamsplitter.
 4. The apparatus of claim 1, wherein said power detectionmeans comprises:a non-polarizing beamsplitter transmitting a transmittedportion of an intermediate beam along said optical path from saidattenuation means, and reflecting a reflected portion of saidintermediate beam away from said optical path; and a power detectiontransducer receiving as an input said reflected portion of saidintermediate beam and producing an output indicating a power levelthereof.
 5. The apparatus of claim 1:wherein said first and secondoptical paths extend from said first beamsplitter in a first direction,being spaced apart and parallel; wherein a plane of reflection withinsaid first beamsplitter extends in said first direction midway betweensaid first and second optical paths; wherein said laser beam is directedat said plane of reflection with a 45-degree angle on incidence thereto;and wherein said first beam directing means includes a first reflectivesurface at which said transmitted beam is directed at a 67.5 degreeangle of incidence and a second reflective surface at which saidreflected beam is directed at a 67.5 degree angle of incidence.
 6. Theapparatus of claim 1, wherein said second beam directing meansincludes:a first reflective surface directing said first output beamtoward said first side of said first disk, wherein said first reflectivesurface is adjustable to vary a first radius on said disk at which saidfirst output beam strikes said disk; and a second reflective surfacedirecting said second output beam toward said second side of said firstdisk, wherein said second reflective surface is adjustable to vary asecond radius on said disk at which said second output beam strikes saiddisk.
 7. The apparatus of claim 6:wherein each said reflective surfaceis pivotally adjustable on a stage; being positioned so that a beam fromsaid optical path, reflected at said disk, is not returned along saidoptical path, and wherein each said stage is adjustable in a directionperpendicular to an adjacent surface of said first disk.
 8. Theapparatus of claim 1, comprising additionally:a beam expander throughwhich said laser beam passes to form a slightly divergent expanded beam;a first focussing lens in said first optical path to focus said firstoutput beam on said first side of said disk; and a second focussing lensin said second optical path to focus said second output beam on saidsecond side of said disk.
 9. The apparatus of claim 8, wherein each saidfocussing lens is adjustable along said optical path for beam focussingextending therethrough and in a plane perpendicular to said optical pathfor beam centering within said focussing lens.
 10. The apparatus ofclaim 1, comprising additionally:third beam directing means fordirecting said first output beam along a third optical path to a firstside of a second disk and for directing said second output beam along afourth optical path to a second side of said second disk: and a movablemirror assembly movable between a first position in which said outputbeams are directed therefrom along said first and second optical pathsand a second position in which said output beams are directed therefromalong said third and fourth optical paths.
 11. Apparatus for directingportions of a laser beam simultaneously at opposite sides of a firstdisk being textured by pulses from said laser beam, wherein saidapparatus comprises:a first beamsplitter dividing said laser beam intotransmitted and reflected beams, wherein said first beamsplitterincludes a reflective surface as a 45-degree angle of incidence withsaid laser beam; a first steering mirror having a 67.5-degree angle ofincidence with said transmitted beam, reflecting said transmitted beamto extend along a first optical path in a first direction; a secondsteering mirror having a 67.5-degree angle of incidence with saidreflected beam, reflecting said reflected beam to extend along a secondoptical path, parallel to said first optical path, in said firstdirection; and output beam directing means for directing saidtransmitted beam along said first optical path to a first side of saidfirst disk and for directing said reflected beam along said secondoptical path to a second side of said first disk, opposite said firstside thereof.
 12. The apparatus of claim 11, wherein said output beamdirecting means includes:a first reflective surface directing said firstoutput beam toward said first side of said first disk, wherein saidfirst reflective surface is adjustable to vary a first radius on saiddisk at which said first output beam strikes said disk; and a secondreflective surface directing said second output beam toward said secondside of said first disk, wherein said second reflective surface isadjustable to vary a second radius on said disk at which said secondoutput beam strikes said disk.
 13. The apparatus of claim 12:whereineach said reflective surface is pivotally adjustable on a stage; beingpositioned so that a beam from said optical path, reflected at saiddisk, is not returned along said optical path, and wherein each saidstage is adjustable in a direction perpendicular to an adjacent surfaceof said first disk.
 14. The apparatus of claim 11, comprisingadditionally:a beam expander through which said laser beam passes toform a slightly divergent expanded beam; a first focussing lens in saidfirst optical path to focus said first output beam on said first side ofsaid disk; and a second focussing lens in said second optical path tofocus said second output beam on said second side of said disk.
 15. Theapparatus of claim 14, wherein each said focussing lens is adjustablealong said optical path for beam focussing extending therethrough and ina plane perpendicular to said optical path for beam centering withinsaid focussing lens.
 16. The apparatus of claim 11, comprisingadditionally:third beam directing means for directing said first outputbeam along a third optical path to a first side of a second disk and fordirecting said second output beam along a fourth optical path to asecond side of said second disk: and a shuttling mirror assembly movablebetween a first position in which said output beams are directedtherefrom along said first and second optical paths and a secondposition in which said output beams are directed therefrom along saidthird and fourth optical paths.